High-Pressure Discharge Lamp

ABSTRACT

A high-pressure discharge lamp may include a ceramic elongated discharge vessel with a central part and two ends and an axis, the ends being sealed by means of seals, electrodes, which extend into the discharge volume enveloped by the discharge vessel, being anchored in the seals at leadthroughs, and the leadthroughs being sealed in the seal by means of glass solder, and a fill being accommodated in the discharge volume, wherein a cover rests on at least one end of a seal, which has a hollow-cylindrical body which is matched to the diameter of the seal, the cover covering at least exposed glass solder.

TECHNICAL FIELD

The invention is based on a high-pressure discharge lamp in accordancewith the precharacterizing clause of claim 1. Such lamps are inparticular high-pressure discharge lamps with a ceramic discharge vesselfor general lighting.

PRIOR ART

U.S. Pat. No. 4,970,431 has disclosed a sodium high-pressure dischargelamp, in which the bulb of the discharge vessel is manufactured fromceramic. Fin-like protrusions used for heat dissipation are plugged ontothe cylindrical ends of the discharge vessel.

EP-A 506 182 has disclosed coatings consisting of graphite or carbon orthe like which are applied to ceramic discharge vessels at the ends inorder to have a cooling effect.

A nitrogen fill in the outer bulb for reducing the temperature of thelamp in question is also known, see EP 581 423, for example. Photometricdata are negatively influenced thereby, however.

DESCRIPTION OF THE INVENTION

The object of the present invention is to provide a high-pressuredischarge lamp, in which local heating of the discharge vessel islargely avoided.

This object is achieved by the characterizing features of claim 1.

Particularly advantageous configurations are given in the dependentclaims.

The high-pressure discharge lamp is equipped with a ceramic elongateddischarge vessel, usually consisting of Al₂O₃ or else AlN. The dischargevessel defines a lamp axis and has a central part and two end regions,which are each sealed by seals in the form of capillaries, electrodes,which extend into the discharge volume enveloped by the dischargevessel, being anchored in the seals. Preferably, the discharge volumealso contains a fill with metal halides. This applies in particular tometal halide lamps which contains at least one of the halides of therare earth metals, preferably one of the elements Dy, Ho, Tm, inparticular together with Ce, in particular together with the halide ofNa. In this case, color temperature fluctuations occur readily as aresult of distillation effects.

Within reflector lamps, reflectors or else in narrow luminaires in whichlamps with a base at one or two ends are used, or else in very compactlamps with an outer bulb, undesirable local temperature increases mayarise as a result of back-reflection of radiation portions of specificcomponents, for example of a cylindrical reflector neck region, onto thecapillary of the discharge vessel. Damage to the sealing material,usually a glass solder, which seals the system including the ceramiccapillary/electrode system may result. Fill constituents may emerge fromthe burner. According to the invention a cover is positioned onto theregion where the glass solder is revealed on the outside for shieldingpurposes. The cover is preferably a sleeve or else a coating consistingof metal or metal oxide.

Since the radiation portion which is reflected back from the outside isshielded by the coating or sleeve, local heating of the fuse-seal zonecan be avoided or reduced.

Specifically, the invention relates to a discharge lamp with a ceramicdischarge vessel with capillaries, in which electrode systems arefuse-sealed. The length of the capillaries and the geometry of thedischarge vessel can vary. The geometry of the discharge vessel can inthis case be cylindrical, round, elliptical or the like.

A novel possibility for radiation shielding is the use of a sleeveconsisting of ceramic, preferably consisting of steatite ceramic. It isshaped in such a way that it covers at least the entire fuse-sealregion. This shielding sleeve is a hollow cylinder, which is turned backover the fuse-seal region of the ceramic capillary. The sleeve isprevented from sliding on the capillary by virtue of suitable measureswhich produce a holding mechanism, for example flat pinch-sealing of themetallic power supply line, welding of the stop wire etc. Preferably,the shielding sleeve has a bottom which covers the glass solder.However, it can also be extended to a sufficient extent only beyond theend of the capillary, in a simpler manner.

In particular, in addition a high-temperature-resistant, preferablyceramic coating can be applied to the fuse-seal zone of the burnercapillary, as is known per se. Particularly well suited is zirconiumoxide or another metal oxide. EP-A 506 182 has disclosed coatingsconsisting of graphite or carbon or the like which are applied toceramic discharge vessels at the ends in order to have a cooling effect.The application of the coating can take place by means of vapordeposition, atomization, immersion, daubing etc. The layer has goodreflection properties in the visible and infrared radiation ranges. Ahighly reflective, metallic coating is likewise conceivable, however.The position of the coating can extend over the entire fuse-seal regionof the capillary, or else be applied in segmented fashion.

The wall thickness d of the shielding sleeve is between 0.5 and 2 mm.The outer diameter results correspondingly. The length L of the sleeveis preferably from 1 to 1.3 times the fuse-seal zone.

In principle, other materials than steatite ceramic are alsoconceivable. The sleeve is preferably simply in the form of a cylinder.However, other embodiments can also be used. One possible variantembodiment may be a temperature-stable, preferably ceramic sleeveprovided on the outside with ribs and/or webs. In this case, thearrangement of these ribs or webs can have an axial or else radialprofile. The ribs or webs can be either continuous or in segmented form.

The number of ribs or webs is dependent on the diameter of the burnercapillary or the sleeve and on the profile of the webs (axial orradial). In the case of an axial profile of the webs, the number is atleast three webs, however. They are preferably distributed uniformlyover the circumference. In the case of a radial profile of the webs, agap of at least from one to three times the web width is preferred inrelation to the neighboring web. The width of the web in the case of theaxial profile is dependent on the outer diameter of the sleeve and onthe number of webs, but is at least 0.5 mm. The depth of the webs is atleast 0.5×d, at most 3×d (d is the wall thickness of the sleeve).

In this variant embodiment, a combination with a coating is alsoconceivable. The coating should be reflective. Suitable materials are inparticular ZrO₂ or TiO₂, but metal layers which are resistant to hightemperatures are also conceivable. This coating can also be used per seon its own, i.e. without a sleeve, in particular by virtue of itcovering the exposed meniscus of the glass solder.

A further possibility which is already known for reducing thetemperature in the fuse-seal region is the introduction of the webs orribs directly into the material of the burner ceramic; see WO2007082885.In this case, various geometries can likewise be used. One disadvantageis the fact that the glass solder on the outside cannot be covered by anintegral web.

A modified capillary end geometry can result in a reduction in thecapillary temperature in the fuse-seal zone.

In particular, the seals are advantageously in the form of capillaries.However, they can also have a different design; see DE-A 197 27 429, forexample, in which a cermet pin is used.

The discharge vessel typically consists of aluminum-containing ceramicsuch as PCA or else YAG, AlN or AlYO₃. The choice of fill is not subjectto any particular restrictions either.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below with reference to aplurality of exemplary embodiments. In the figures:

FIG. 1 shows a high-pressure discharge lamp with a discharge vessel;

FIG. 2 shows a detail of the discharge vessel shown in FIG. 1;

FIGS. 3-4 show an exemplary embodiment of an end region of a dischargevessel;

FIGS. 5-6 each show a further exemplary embodiment of a dischargevessel.

PREFERRED EMBODIMENT OF THE INVENTION

FIG. 1 shows a schematic of a metal halide lamp 1. It includes a tubulardischarge vessel 2 consisting of ceramic, into which two electrodes areintroduced (not shown). The discharge vessel has a central part 5 andtwo ends 4. Two seals 6, which are in this case in the form ofcapillaries, rest on the ends. Preferably, the discharge vessel and theseals are produced integrally from one material such as PCA.

The discharge vessel 2 is surrounded by an outer bulb 7, which isterminated by a base 8. The discharge vessel 2 is held in the outer bulbby means of a frame, which contains a short and a long power supply line11 a and 11 b.

FIG. 2 shows a detail of a discharge vessel. A leadthrough 9 consistingof a plurality of parts rests in the capillary 6, as is known per se.Said leadthrough is in the form of an Mo bar 11, with an Mo filament 12being applied in the front half thereof in order to minimize the gapwith respect to the capillary. The shaft 13 of the electrode 14 rests atthe front on the Mo bar. A glass solder 19, which forms a meniscustowards the outside, is used for sealing purposes at the end of thecapillary. The glass solder in this case runs into the capillary, forexample as far as the point at which the Mo filament 12 begins. Thisregion is denoted as the sealing length L.

The shield should now be fitted in such a way that it, if possible,protects the sealing length and the glass solder positioned on theoutside. In principle, as is shown below in FIG. 2, even a coating 20 issuitable for this purpose, said coating firstly shielding the sealinglength L and in addition also the glass solder 19 on the outside. Saidcoating is manufactured from a highly thermally resistant metal oxidesuch as zirconium oxide or titanium oxide or aluminum oxide, as is knownper se.

FIG. 3 shows an end region, in which a shielding sleeve 25 has beenplugged onto the end of the capillary 6. The sleeve 25 has ahollow-cylindrical body 26, which is matched, from the outside,approximately to the diameter of the capillary. In addition, the sleeve25 has a bottom part 27, which seals the body 26 with respect to theoutside and therefore covers the glass solder 19 which is on theoutside. In order that it can be threaded onto the leadthrough 9, thebottom has a central bore 28. The sleeve can itself be surrounded by acoating 21, as specified above, which preferably extends over the bodyand the bottom or else only over the body or a part thereof. The sleeveis held by virtue of flat pinch-sealing 19 of the leadthrough 9 or thelike. The sleeve should cover at least the sealing length L of the glasssolder.

FIG. 4 shows a simple version of the sleeve 30 in which no bottom isprovided. Shielding of the glass solder 19 positioned on the outside isachieved by virtue of the fact that the hollow cylinder is extendedbeyond the glass solder and thus provides shading with respect toincident radiation. In this case, the sleeve should be fastened on thecapillary by means of adhesive or fused ceramic 40 or the like. For thispurpose, it is recommended to provide channels 31 for accommodating theadhesive on the inner wall of the sleeve.

FIG. 5 shows a sleeve 33 which has been provided with radial ribs 34 inorder to improve the emission of heat. FIG. 6 shows a sleeve 35, whichhas been provided with axial webs 36 in order to improve the emission ofheat. In this case, too, a coating is additionally possible. The numberof ribs or webs is dependent on the diameter of the burner capillary orthe sleeve and on the profile of the webs (axial or radial). In the caseof an axial profile of the webs, the number of webs which aredistributed uniformly over the circumference is at least three, however.In the case of a radial profile of the webs, a gap 47 of at least 1-3times the web width is provided with respect to the neighboring web. Thewidth 48 of the webs in the case of the axial profile is dependent onthe outer diameter of the sleeve and on the number of webs, but is aminimum of 0.5 mm. The depth 49 of the webs is a minimum of 0.5×d, amaximum of 3×d (wall thickness of sleeve). LX is the total length of thesleeve.

The point of attachment, wall thickness and height of the cooling ringcan be used to adjust the cooling effect on the surface zone of theburner vessel locally and to adapt it to the respective requirements.

The point of attachment of the sleeve, the wall thickness and the lengthof the sleeve as well as the thickness of the bottom can be used tooptimize the thermal capacity.

1. A high-pressure discharge lamp, comprising: a ceramic elongateddischarge vessel with a central part and two ends and an axis, the endsbeing sealed by means of seals, electrodes, which extend into thedischarge volume enveloped by the discharge vessel, being anchored inthe seals at leadthroughs, and the leadthroughs being sealed in the sealby means of glass solder, and a fill being accommodated in the dischargevolume, wherein a cover rests on at least one end of a seal which has ahollow-cylindrical body which is matched to the diameter of the seal,the cover covering at least exposed glass solder.
 2. The high-pressuredischarge lamp as claimed in claim 1, wherein the seal is in the form ofa capillary.
 3. The high-pressure discharge lamp as claimed in claim 1,wherein the sleeve protrudes outwards beyond the seal to such an extentthat it acts as shading means for the glass solder located on theoutside.
 4. The high-pressure discharge lamp as claimed in claim 1,wherein the sleeve is sealed off from the outside by means of a bottom.5. The high-pressure discharge lamp as claimed in claim 1, wherein thesleeve is manufactured from ceramic.
 6. The high-pressure discharge lampas claimed in claim 1, wherein in that the sleeve has ribs or webs onthe outside for improving the cooling effect.
 7. The high-pressuredischarge lamp as claimed in claim 1, wherein the sleeve is additionallyprovided at least partially with a heat-reflective coating.
 8. Thehigh-pressure discharge lamp as claimed in claim 1, wherein the cover isrealized by a coating consisting of metal oxide.
 9. The high-pressuredischarge lamp as claimed in claim 1, wherein the fill contains metalhalides.
 10. The high-pressure discharge lamp as claimed in claim 1,wherein the cover rests on a separate sleeve
 11. The high-pressuredischarge lamp as claimed in claim 1, wherein the cover also covers afurther region of the seal which contains glass solder.
 12. Thehigh-pressure discharge lamp as claimed in claim 5, wherein the sleeveis manufactured from steatite.
 13. The high-pressure discharge lamp asclaimed in claim 1, wherein the cover is realized by a coatingconsisting of metal.